835 



Abstract— Fishes are widely known 

 to aggregate around floating objects, 

 including flotsam and fish aggregating 

 devices (FADs). The numbers and diver- 

 sity of juvenile fishes that associated 

 with floating objects in the nearshore 

 waters of the eastern tropical Pacific 

 were recording by using FADs as an 

 experimental tool. The effects of fish 

 removal. FAD size, and the presence 

 or absence of a fouling community at 

 the FAD over a period of days, and the 

 presence of prior recruits over a period 

 of hours were evaluated by using a 

 series of experiments. The removal of 

 FAD-associated fish assemblages had a 

 significant effect on the number of the 

 dominant species (Abudefduf troschelii) 

 in the following day's assemblage com- 

 pared to FADs where the previous day's 

 assemblage was undisturbed; there was 

 no experimental effect on combined spe- 

 cies totals. Fishes do, however, discrimi- 

 nate among floating objects, forming 

 larger, more species-rich assemblages 

 around large FADs compared to 

 small ones. Fishes also formed larger 

 assemblages around FADs possessing 

 a fouling biota versus FADs without a 

 fouling biota, although this effect was 

 also closely tied to temporal factors. 

 FADs enriched with fish accumulated 

 additional recruits more quickly than 

 FADs that were not enriched with fish 

 and therefore the presence of prior 

 recruits had a strong, positive effect on 

 subsequent recruitment. These results 

 suggest that fish recruitment to float- 

 ing objects is deliberate rather than 

 haphazard or accidental and they sup- 

 port the hypothesis that flotsam plays 

 a role in the interrelationship between 

 environment and some juvenile fishes. 

 These results are relevant to the use 

 of FADs for fisheries, but emphasize 

 that further research is necessary for 

 applied interests. 



Marine fish assemblages associated with 

 fish aggregating devices (FADs): 

 effects of fish removal, FAD size, 

 fouling communities, and prior recruits 



Peter A. Nelson 



Department of Biological Sciences 



Northern Arizona University 



Flagstaff, Arizona 86011-5640 



Present address: Center for Marine and Biodiversity & Conservation 



Scripps Institution of Oceanography 



University of California, San Diego 



La Jolla, California 92093-0202 

 E-mail address, pnelson@ucsd.edu 



Manuscript approved for publication 

 13 June 2003 by Scientific Editor. 



Manuscript received 26 June 2003 



at NMFS Scientific Publications Office. 



Fish. Bull. 101:835-850 



Fishes associate with floating objects 

 in nearly all oceans of the world (Good- 

 ing and Magnuson, 1967; Hunter and 

 Mitchell, 1967; Klima and Wickham, 

 1971; Crawford and Jorgenson, 1993; 

 Kingsford, 1993; Druce and Kingsford, 

 1995; Massuti et al., 1998; Hampton 

 and Bailey, 1999; Parin and Fedoryako, 

 1999). Fishes also gather around fish 

 aggregating devices (FADs), floating 

 objects deployed to concentrate target 

 species or bait fishes and improve the 

 catch for artisanal, sport, or commercial 

 fisheries. The physical attributes of a 

 floating object, such as a FAD, may affect 

 the ability of potential fish recruits to 

 locate the floating object or may affect 

 the adaptive advantages of associating 

 with that object (or both) — a topic that 

 has been addressed in numerous prior 

 studies (e.g. Hunter and Mitchell, 1968; 

 "Wickham et al., 1973; Wickham and 

 Russell, 1974; Fedoryako, 1989; Roun- 

 tree, 1989; Safran, 1990; Safran and 

 Omori, 1990; Friedlander et al., 1994; 

 Hall et al., 1999b). However, the present 

 study is apparently the first to address 

 empirically the effects of disturbance, 

 fouling communities, and prior recruits 

 by examining both the number and 

 the diversity of fishes that aggregate 

 around FADs. In addition, this study 

 addresses the effect of FAD size, a factor 

 well represented in prior studies but 

 frequently confounded by temporal or 

 design issues. FADs are widely used to 

 enhance sport and commercial fisheries, 

 but are expensive to build, deploy, and 

 maintain; therefore better information 



about the effects of FAD size and foul- 

 ing could aid design efforts. Given the 

 bycatch associated with the FAD fishery 

 for tuna in the eastern tropical Pacific 

 (Hall et al., 2000), for example, we need 

 a better understanding of how fishes 

 use FADs in order to manage fisheries 

 for FAD-associated species (Lennert- 

 Cody and Hall, 2000). Finally, careful 

 study of how differing characteristics 

 of floating objects affect fish recruit- 

 ment may provide important clues 

 regarding the adaptive significance of 

 fish associations with flotsam and drift 

 algae — a phenomenon widely noted but 

 poorly understood. 



Prior research has suggested that 

 rates of immigration and fish removal 

 from FADs similar to those seen in the 

 present study were high from one day to 

 the next (Nelson, 1999), and "Wickham 

 and Russell (1974) reported that mid- 

 water FADs, which were fished daily, 

 produced a larger cumulative catch 

 than mid-water FADs, which were un- 

 disturbed during the same period and 

 then fished once at the end of the con- 

 clusion of the study. I tested the hypoth- 

 esis that, over time, the size and diver- 

 sity of FAD-associated fish assemblages 

 are reduced by the repeated removal of 

 these fishes compared with undisturbed 

 assemblages. Effective management 

 or use of FADs deployed for fisheries 

 purposes and an understanding of the 

 ecological relationship between flotsam 

 and fishes associated with flotsam will 

 depend in part on patterns of immigra- 

 tion and loss to fish assemblages. 



